The overall aim of this continuing investigation in a well characterized, community-based population sample of children and adults is to study prospectively factors that modify growth and decline inpulmonary function and to identify predictors of chronic obstructive lung disease (COLD) in adult life. Extensive longitudinal information on respiratory symptoms and illnesses, cigarette smoking, demographic and household factors and measurements of pulmonary function have already been obtained on the cohort. Existing data on these factors will be supplemented by additional observations on them and by the investigation of: 1) indices of airways responsiveness (methacholine challenge, ratio of volumn specific flows derived for maximum and partial expiratory flow volume curves); and 2) indices of atopy (skin prick tests, total and antigen-specific IgE); and 3) indices of inflammation (eosinophil and leukocyte counts). Data will be collected in alternate years on half the population under study and will provide approximately 2000 person-years of observation on the cohort between ages 20-35, a period when maximal lung function level and onset of decline will occur. A variety of parametric (autoregressive and random effects) and nonparametric (smoothers) models will be used to assess ths longitudinal nature of the data in particular in regard to changes in lung function level but also for categorical symptom data. The results of these investigations should provide insights into the susceptability for the development of chronic obstructive lun8 disease hereby helping us identify individuals at increased risk of smoking. This information can then be used in the public health sphere to develop additional strategies for prevention of this important disease.